Insulated runner system for plastic cap molds

ABSTRACT

In extrusion molding of plastic screw caps, the unit cap cost can be closely related to the number of caps which can be made at each cycle of the mold operation. A system is described which maximizes the number of caps by providing hot, self-insulated runners which feed a number of relatively short sprue channels with hot plastic so that a larger number of caps than before can be molded in a single cycle without the remoter caps at the edges of the die being fed plastic too cool to permit successful caps to be molded.

United States Patent [191 Kessler INSULATED RUNNER SYSTEM FOR PLASTICCAP MOLDS [76] Inventor: Milton Kessler, 6690 Harrington,

Youngstown, Ohio [22] Filed: June 26, 1972 21 Appl. N6; 266,365

Related US. Application Data [62] Division of Ser. No. 61,766, Aug. 6,1970,

[1 1 3,776,676 Dec. 4, 1973 10/1970 Segrnuller 249/110 X OTHERPUBLICATIONS Pye, lnjection Mold Design, pp. 145-147, 1968, PlasticsInstitute, London, England.

Glanvill et al., Injection-Mould Design Fundementals. pp. 143-144, 1965.

Primary Examiner-J. Spencer Overholser Assistant Examiner-John E.Roethel Attorney-Max L. Libman [5 7 ABSTRACT In extrusion molding ofplastic screw caps, the unit cap cost can be closely related to thenumber of caps which can be made at each cycle of the mold operation. Asystem is described which maximizes the number of caps by providing hot,self-insulated runners which feed a number of relatively short spruechannels with hot plastic so that a larger number of caps than beforecan be molded in a single cycle without the remoter caps at the edges ofthe die being fed plastic too cool to permit successful caps to bemolded.

2 Claims, 8 Drawing Figures PMENIEDUHZ 4mm SHEET 2 [IF 3 FIG. 3.

INVENTOR Milton Kessler flaw OZ/WM.

ATTORNEY PATENTED 41973 INVENTOR Milton Kess/er BY Zim- ATTORNEY 1INSULATED RUNNER SYSTEM FOR PLASTIC CAP MOLDS This is a division ofapplication Ser. NO. 61,766, filed Aug. 6, 1970, now abandoned.

Plastic screw caps are used literally by the hundreds of millions asclosures for all kinds of bottled household goods such as detergents,liquid wax, hand lotions, etc., and although they are very inexpensive,they are still sold by the manufacturer of such caps largely on a pricebasis. It is therefore important that the unit cost of such caps shallbe kept down to a minimum. The caps are typically made of thermoplasticmaterial Therefore extrusion molding, wherein the thermoplastic materialin practically liquid form is forced at high pressures and temperaturesinto a mold which is formed in two major parts, one of which isstationary and contains a major portion of the mold cavities, and theother of which is movable, so that after the caps have been formed andhave cooled sufficiently to retain their shape, the mold can beautomatically opened and the formed caps ejected, Of course, the largerthe number of caps that can be made in a single operation, the smallerwill be the unit cap cost. Thereore, the cap mold will be made with asmany cap cavities as possible; however, the plastic must be fed to thesecap cavities through sprues which are typically formed in either thestationary or movable face of the mold as channels through which themolten plastic material is supplied to the individual cavities. As theseare rather thin channels, they also cool as the newly molded caps cool,and the sprues must therefore also be ejected after each molding cycleof the machine. This material is not wasted, as it can be re-used bybeing added to a subsequent feed batch, since the thermoplastic materialcan be readily remelted.

In order that the newly-formed caps may become sufficiently hardened orset so that they can be quickly removed from the mold, the mold istypically watercooled in order to carry off the excess heat and permitrapid setting of the thermoplastic material. This cooling also affectsthe sprues through which the material is supplied to the individual capmolds, and this also provides a limitation on the number of individualcap cavities which can be placed on a given mold, since if the sprue istoo long, the plastic has cooled sufficiently by the time it gets to theend of the sprue, so that the material is too stiff for successfulmolding of the caps, and this constitutes a limitation on the number ofcap cavities which can be placed on a single mold, and therefore on thenumber of caps which can be made in a single cap cycle.

It is a major object of the present invention to overcome the abovedifficulty, and to provide a system whereby the number of cap cavitieson a given die plate can be increased without any. major changes in themolding equipment. This is accomplished essentially by using a largernumberof shorter sprues, each of which is supplied through aself-insulated runner or feed channel of sufficiently great diameter sothat the plastic flowing in the runner becomes chilled and stiff at thecircumference or periphery of the runner, thus providing in effect aninsulated tube, at the center of which the plastic remains sufficientlywarm to flow freely to the individual sprues at a sufficiently hightemperature that even the outer caps can be successfully molded.

The specific nature of the invention, as well as other objects andadvantages thereof, will clearly appear from a description of apreferred embodiment as shown in the accompanying drawings, in which:

FIG. 1 is a transverse sectional view through a portion of a moldaccording to the invention, showing a single insulated runner,associated sprue, and cap cavities, in the initial molding stage, duringthe period when the cap material is becoming set sufficiently forwithdrawal from the mold;

FIG. 2 shows the same mold during the initial stage of withdrawal of theformed caps from the mold, and immediately prior to ejection of thesprue;

FIG. 3 shows the action immediately after FIG. 2, when the spure hasbeen initially ejected or separated from the mold, and ejection of thecap is about to be- FIG. 4 shows the action after the cap has beencompletely separated from the mold and is about to fall away from themold by gravity;

FIG. 5 shows one of the stationary plates of the mold containing a halfsection of the insulated runner channels;

FIG. 6 shows the mating plate to that shown in FIG. 5, showing the otherhalf section of the stationary insulated runner channe;

FIG. 7 is a sectional view of the two assembled plates of FIGS. 5 and 6taken on line 7-7; and

FIG. 8 is a face view of the mold shown in FIG. 7, showing theconfiguration of all of the mold cavities.

The mold comprises a stationary mold plate made up of two halves 2 and3, suitably fastened together as by bolts, 5 and each containingone-half of the insulated runner channels designated at 4 in FIG. 5 and7 in FIG. 6, so that when these two surfaces are put together, as shownin FIG. 7, they provide circular channels into which plastic is fedthrough supply channel 6 from a conventional plastic extruder which isnot shown. This plastic material is supplied at sufficiently hightemperature and pressure, so that it is in a fluid-like form, andrapidly fills the runner channels 4, 7, which are shown as having sixrunner arms, although it will be apparent that any convenient number ofsuch arms can be used. At the remote end of each of these arms there isan aparture 8 in mold plate 3, through'which the plastic flows via atapered runner lead 8a into the system of sprue channels 9 as indicatedin FIG. 8. As will be seen from FIG. 1, the major portion of the spruechannel 9 is shown formed in movable mold plate 13, but part of it maybe cut into the face of stationary die plate 3, or if desired may be cutentirely into movalbe die plate 13. The sprue channels 9 are connectedat intervals along their length by tapered lead channels 9a to the upperportion of cavities 10 formed in plate 3. In addition, small lateralcavities 9b (FIG. 8) are formed in plate 13, but these are only for thepurpose of balancing the plastic flow, to insure proper distribution ofthe plastic material to the cap cavities, and are not part of thepresent invention. It will thus be seen that during the period when theparts are in the relative position shown in FIG. 1, hot plastic isforced into all of the cap cavities, and the initial stage of the cyclehas begun. The old parts remain in the position shown in FIG. 1 for asufficient time for the plastic material to set; to facilitate this, thedie is usually water-cooled, but since this is conventional, it is notshown in the drawings. In a typical case, a complete cycle may take inthe order of 10 to 20 seconds, most of which time isthe cooling timerequired for the plastic to set.

After the caps have set sufficiently, the backing die plate 14 begins tomove away from the stationary plate, by means of conventional machineryacting on the plate through suitable elements indicated by cylindricalrod 18, a number of which will be attached to the backing plate. Themeans for accomplishing this are part of commercially developed moldingequipment and need not be described here. It will be noted that theinteriors of the caps have been molded about the threaded ends 15a ofstuds 15 which are screwed or otherwise fastened to movable plate 14 andwhich extend loosely on a reduced diameter through movable plate 13. Thecaps are therefore pulled out of the mold cavities 10, being therebyseparated from the tapered sprue lead 9a at the orifice of smalldiameter through which plastic is fed to the cap mold. At the same time,the sprue 9 adheres sufficiently to plate 13 so that it is also pulledback with plate 13 and is also separated from the large supply channel 47 at the smallest diameter of the sprue feed channel 9a. The crosssection of the sprue at this plane therefore assumes the shape shown inFIG. 2, and the sprue has now been separated from the individual caps;however, the aprue is still carried by plate 13 and must be ejectedtherefrom. A sprue ejector rod 19 is provided, which is slidable inplates 13 and 14 and has an enlarged head 19a which is bottomed with respect to plate 13 by means of spraying 19b. In the position shown inFIG. 2, the bottomed end of rod 19 engages a stationary portion of themachine as indicated at 21 so that this rod cannot move any further tothe right, while the plates 13 and 14 continue moving into the positionshown in FIG. 3, where lug 13a of plate 13 engages a fixed stop 22.Since rod 19 has not been able to move during this part of the motion,it therefore v strips the sprue away from plate 13 as indicated in FIG.3. The sprue now begins to fall by gravity toward the bottom of themold.

Due to the cooling of plates 2 and 3, the plastic material in the runnerchannel 4, 7, will also solidify to some extent near the periphery ofthe channel, as shown at 17, but the diameter of the channel issufficiently great so that the material in the interior of the channelremains liquid as indicated at 17a, and does not solidify due to thefact that the hardened material 17 forms in effect a layer of thermalinsulation which keeps the material at the center of the channel atsufficiently high temperature so that it does not stiffen or set. Thiscondition persists long enough so that the material at the center isstill molten when the caps and sprues have been ejected and the partsreturned to their position shown in FIG. 1 ready for the next cycle ofoperation. It will be seen that the runners thus formed areselfinsulated, and permit an uninterrupted supply of molten plasticmaterial to be furnished to the cap cavities for succeeding cycles ofoperation. Of course, when a given run is completed and the materialstops flowing through the channels 4, 7 for a sufficient length of time,the runner becomes entirely hardened; therefore, before the next batchcan be started the two sections 2 and 3 must be separated and thehardened runner removed.

Continuing with the operation of the molding cycle,

in the position of FIG. 3, the plate 13 is now stopped from furthermotion to the right by engagement of ears 13a (there being several ofthese around the periphery of the plate) with stop 22, so thatas plate14 continues to move to the right in the position of FIG. 4. the

threaded end of studs 15 is stripped from the individual caps as shownin FIG. 4, which can be done without destroying the interior thread ofthe cap because the cap is still in a relatively soft and warm conditionand therefore has sufficient elasticity to permit the threads to beundamaged during the stipping operation. Very shortly thereafter, as thecooling process continues, the plastic material become sufficientlyrigid so that such stripping would be impossible since some deformationof the interior must occur during this process, but the caps in practiceretain sufficient elastic memory to resume their original interiorconfiguration with the interior thread undamaged. It will be seen thatin the position of FIG. 4, the caps are no longer supported and canbegin to fall along with the sprue, which has already begun to fall tothe bottom of the mold, where the parts are collected by suitableconventional equipment which are not part of the present invention.

Since in practice there are various guide rods (not shown) which keepthe movable and stationary parts of the mold in alignment, it is anadvantage of the shorter sprues made possible by the present invention,that they can be made sufficiently small to fall clear of such guiderods without becoming entangled therein as would be the case withlonger, more complex sprues.

After the position of FIG. 4 has been reached, continued operation ofthe driving mechanism through cylinder 18 causes the action to bereversed and the plates 14 and 13 to move back into the initial positionof F IG. 1, in preparation for the next cycle. It will be understoodthat the particular stripping means shown are intended only to beexemplary, since the caps and sprues can be ejected in other ways, aswill be apparent to those skilled in the art. By the use of the presentinvention, a supply of hot material is maintained at a number of pointson the stationary die plate, so that short sprues may be used,permitting a larger number of cap mold cavities to be employed than hastherefore been possible.

I claim:

1. v a. A multiple molding machine for thermoplastic caps comprising astationary portion and a movable portion in abutting surface relationwith cap cavities and sprue channels cut into their abutting surfaces toform mold cavities,

b. said stationary portion comprising two metal blocks having abuttingsurfaces with runner channels cut into said surfaces,

c. said runner channels branching from a common feed inlet aperture to anumber of short runner branches of large diameter, all supplied inparallel from the common inlet aperture,

d. each of said branchesleading to an inlet of a separate spure channelcut into the abutting surfaces of said stationary and movable portions,

e. each said sprue channel unit branching from said last inlet to anumber of short sprue channels supplied in parallel through said inlet,

f. each said short sprue channel supplying a number of cap cavities cutinto said last abutting surfaces by means of tapered sprue leads runningfrom said sprue channels to the top portion of said cap cavities,

g. means for supplying thermoplastic material under pressure throughsaid runner feed inlet aperture to said cap cavities,

6 h. means for cooling said mold until the thermoplasmovable plate andmeans for withdrawing said tic material in the sprue and cap cavitieshas hardmovable plate from said stationary portion to sepaenedsufficiently to be ejected from the mold, rate the hardened caps andsprue material, carried i. said runner channels being of sufficientlylarge diby said plate, from said cap cavities and sprue ameter so thatthe plastic material in them is hard- 5 channels, and for separatingsaid sprue material ened by said cooling only at a layer adjacent thefrom the caps. surfaces of said channels, to form an insulating k. sprueejector rod means passing through said movlayer of plastic material ofgenerally tube-like con- I able plate for ejecting said sprue materialfrom said figuration at the center of which the plastic matemovableplate during initial travel of said movable rial remains at asufficiently high temperature to 10 plate, flow through the runners tosupply the sprue for l. and means for separating said hardened caps fromsuccessive cycles of operation. said movable plate during continuedtravel of said 2. The invention according to claim 1, movable plate. j.said movable portion of the machine comprising a

1. A. A multiple molding machine for thermoplastic caps comprising astationary portion and a movable portion in abutting surface relationwith cap cavities and sprue channels cut into their abutting surfaces toform mold cavities, b. said stationary portion comprising two metalblocks having abutting surfaces with runner channels cut into saidsurfaces, c. said runner channels branching from a common feed inletaperture to a number of short runner branches of large diameter, allsupplied in parallel from the common inlet aperture, d. each of saidbranches leading to an inlet of a separate spure channel cut into theabutting surfaces of said stationary and movable portions, e. each saidsprue channel unit branching from said last inlet to a number of shortsprue channels supplied in parallel through said inlet, f. each saidshort sprue channel supplying a number of cap cavities cut into saidlast abutting surfaces by means of tapered sprue leads running from saidsprue channels to the top portion of said cap cavities, g. means forsupplying thermoplastic material under pressure through said runner feedinlet aperture to said cap cavities, h. means for cooling said molduntil the thermoplastic material in the sprue and cap cavities hashardened sufficiently to be ejected from the mold, i. said runnerchannels being of sufficiently large diameter so that the plasticmaterial in them is hardened by said cooling only at a layer adjacentthe surfaces of said channels, to form an insulating layer of plasticmaterial of generally tube-like configuration at the center of which theplastic material remains at a sufficiently high temperature to flowthrough the runners to supply the sprue for successive cycles ofoperation.
 2. The invention according to claim 1, j. said movableportion of the machine comprising a movable plate and means forwithdrawing said movabLe plate from said stationary portion to separatethe hardened caps and sprue material, carried by said plate, from saidcap cavities and sprue channels, and for separating said sprue materialfrom the caps. k. sprue ejector rod means passing through said movableplate for ejecting said sprue material from said movable plate duringinitial travel of said movable plate, l. and means for separating saidhardened caps from said movable plate during continued travel of saidmovable plate.